boom (n.1)

"long pole," 1640s, specifically, "long spar run out from a ship" (1660s), from Scottish boun, borrowed from Dutch boom "tree, pole, beam," from a Middle Dutch word analogous to German Baum, English beam (n.). As "movable bar for a microphone or camera," 1931.

boom (n.2)

"loud, deep, hollow, continued sound," c. 1500, from boom (v.). Compare boondi Aboriginal word for waves breaking on a beach (source of Sydney's Bondi Beach), said to be imitative of the sound.

boom (n.3)

"sudden start or increase in commercial or other activity," 1873, sometimes said to be from boom (n.1) in the specific nautical meaning "a long spar run out to extend the foot of a sail" -- a ship "booming" being one in full sail. But it could just as well be from boom (n.2) on the notion of "sudden burst." The verbal sense "burst into sudden activity" seems to be slightly older (1871). Boom town is from 1883. The economic cycle of boom and bust has been so called since 1937.